A heat transfer system such as an adsorption heat pump includes an adsorbent, and employs a heat exchange reactor that utilizes an adsorption/desorption reaction of an adsorbate (such as water or ammonia) to the adsorbent.
Mass transport within the adsorbent is given by (∂c/∂t)=ΔDΔC−(1−ε)ρ(∂q/∂t), and it is hypothesized that diffusion constant D therein is rate limiting for mass transport of water vapor through adsorbent layers in a case in which conventional filling constructions are adopted. Regarding this point, in practice, general adsorbent heat pumps tend to operate with an adsorption rate that is extremely slow (300 seconds to 600 seconds) compared to the intrinsic adsorption rate of the adsorbent of several seconds to several tens of seconds. Output by volume is therefore extremely small.
To improve the low output that occurs due to the limitation on the rate imposed by diffusion as described above, coated adsorption heat pumps have been proposed in which a surface of the heat exchange reactor is coated with adsorbent (see, for example, Hirasawa Ryou et. al., “Development of Novel High Efficiency Adsorbents, (Ex-post) Project Evaluation Report”, (online), April 2009, Industrial Structure Council, Industrial Science and Technology Policy Committee, Evaluation Subcommittee, Internet (URL: http://www.meti.go.jp/poliey/tech_evaluation/e00/03/h20/336.pdf)). Such a heat pump has the following characteristics, and cooling output by volume in the adsorption heat pump is enhanced by these characteristics.
(1) Particle diameter is as small as several μm, and single particle adsorption rates are therefore high.
(2) Intra-layer vapor transport resistance is high, and the vapor transport resistance is therefore lowered by using a coating thickness of approximately 200 μm.
(3) The coating thickness is approximately 200 μm, and heat transfer resistance is therefore low.